Accurate verification of products and documents is critical to a wide variety of industries including the manufacture of pharmaceutical, clothing, automotive parts, and the issuance of credit and identification cards or travel/immigration documentation. Counterfeiters of products, currency and documents have developed increasingly sophisticated methods of detecting and copying of marks and labels.
Counterfeiting and product diversion cost owners of products, brand names, and intellectual property billions of dollars annually on a worldwide basis, according to the International Anti-Counterfeiting Council (IACC). The problem in the United States, for example, encompasses an estimated loss in revenues of $200 billion per year, as well as associated costs in tax revenues and the loss of jobs.
Thus, there is a well-recognized need for tagging, marking and/or labeling for identification purposes, such as those used for product identification, product tracking and anti-theft applications. Such labeling generally is readily detectable by visual means. Bar codes such as are conventionally used in many commercial applications today would be an example of such visible labels.
U.S. Pat. No. 6,402,986 discloses the use of luminescent compositions comprising lanthanide chelates for verification of products or documents.
U.S. Pat. No. 6,165,609 discloses security coatings for labels that cannot be detected by the naked eye, but can be detected by a detector.
The range of goods that need to be verified is large and continuing to grow. Accordingly, there is a continuing need to develop new compositions and methods for product verification and security identification of goods and documents in common use.
A transparent polymer that exhibits a luminescent response would be extremely useful in transparent markers, taggants or labels, or in a number of other potential uses, such as tagged or identifiable packaging film.
Merely blending rare earth oxide or sulfide particles within a polymer matrix would produce a filled polymer material that possessed a luminescent response. However, since the particles are larger than most wavelengths of light, the filled system would scatter incident waves of light resulting in a material that is not transparent.
Rajagopalan, Tsatsas and Risen, Jr. have prepared ionomers of ethylene acrylic acid (EAA) copolymer and ethylene methacrylic acid (EMA) copolymer, in which the copolymers were neutralized with Dy3+, Er3+, Sm3+, Tb3+, Tm3+, and Yb3+, and mixtures thereof. See Rajagopalan, et. al., “Synthesis and Near Infrared Properties of Rare Earth Ionomers”, Journal of Polymer Science: Part B: Polymer Physics, vol. 34, 151-161 (1996). They report that these ionomers have valuable optical properties and that they exhibit strong Raman scattering and luminescence in the near infrared (IR) region.
Polymers containing lanthanide metal ions, specifically Eu3+and Tb3+salts are disclosed in Y. Okamoto, “Synthesis, Characterization, and Application of Polymers Containing Lanthanide Metals”, J. Macromol. Sci.-Chem., A24(3&4), pp. 455-477 (1987). The polymers used include poly(acrylic acid), poly(methacrylic acid), partially sulfonated or carboxylated styrene, styrene-acrylic acid copolymers and methyl methacrylate-methacrylic acid copolymers. The fluorescent intensity of these polymers was studied. The polymers made appear to contain up to 8 weight % Tb3+and up to 10-11 weight % Eu3+, though the fluorescence intensity for the Eu3+-polymer salts reached a maximum at 4-5 weight % Eu3+content.
Paramagnetic polymer compositions comprising lanthanide metal ions, specifically Gd3+, Tb3+, Dy3+, Ho3+, Er3+ and Tm3+, are disclosed in WO02/058084.